Method of making an electron sensitive mosaic color screen

ABSTRACT

A method of making an Electron Sensitive Mosaic Color Screen including the steps of depositing a layer of photoresist material over the face of a tube, mounting a shadow mask having apertures therein in front of the screen, radiating light on the photoresist layer through the apertures from a light source which is gyrating successively about each of the color centers of the tube, developing the photoresist layer to form a plurality of dot locations which are smaller than the mask apertures and thereafter forming selected phosphors at said dot locations.

United States Patent [191v Ohgoshi et al.

[ 1 METHOD OF MAKING AN ELECTRON SENSITIVE MOSAIC COLOR SCREEN [75] Inventors: Akio Ohgoshi, Tokyo; Takuji Inoue,

Kanagawa, both of Japan [73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: July 9, 1971 [21] Appl. No.: 161,085

[30] Foreign Application Priority Data July 11, 1970 Japan 45-60737 [52] US. Cl 96/36.l, ll7/33.5 CM, 117/3'3.5 C, 117/38, 313/92 B, 354/1 [51] Int. Cl G03c 5/00 [58] Field of Search 96/36.1, 45; 313/92 B, 313/92 R; 354/1; ll7/33.5 CM, 33.5 C, 38

[56] 7 References Cited UNITED STATES PATENTS 926,377 6/1909 Albert.... 96/45 2,733,366 2/1956 Grimm et al.... 96/36.1 3,146,368 9/1964 Flore etal. 96/36.1 3,152,900 4/1967 Kaus et a1. 96/36.l 3,222,172 12/1965 Giuffrida 96/36.1

4 1 Dec. 10, 1974 3,558,310 2/1971 Mayaud 96/36.1 3,615,460 10/1971 Lange 96/36.l 3,615,461 10/1971 Kaplan 96/36.l 3,615,462 10/1971 Szegho et al..... 96/36.1 3,725,106 4/1973 Hosokoshi 96/36.1 X FOREIGN PATENTS OR APPLICATIONS 573,621 0/1959 Canada 95/1 R Primary Examiner-David Klein Assistant Examiner-Edward C. Kimlin Attorney, Agent, or Firm-Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [5 7] ABSTRACT A method of making an Electron Sensitive Mosaic Color Screen including the steps of depositing a layer of photoresist material over the face of a tube, mounting a shadow mask having apertures therein in front of the screen, radiating light on the photoresist layer through the apertures from a light source which is gyrating successively about each of the color centers of the tube, developing the photoresist layer to form a plurality of dotlocations which are smaller than the v mask apertures and thereafter forming selected ph0sphors at said dot locations.

4 Claims, 26 Drawing Figures PAIENKLUECIOIWI mm a 7 INVENTOR. A/rm 0/1505/11 BY TAKUJI mow;

METHOD OF MAKING AN ELECTRON SENSITIVE MOSAIC COLOR SCREEN BACKGROUND OF THE INVENTION on the face plate is decreased by the light absorbing layer to provide for enhanced contrast in the reproduced color picture, so that the light transmission factor of the face plate can be increased, as compared with those in conventional color picture tubes, thereby to enable reproduction of the color picture with brightness and with great contrast.

Heretofore, color phosphor screens having such a light absorbing layer have been produced, for example, by the following method. Polyvinyl alcohol (PVA) containing ferric chloride is laid down on the inner surface of the face plate. The polyvinyl alcohol layer at those areas which will ultimately be occupied by red, green and blue phosphor dots is exposed to light through a shadow mask serving as an exposure mask by means of a conventional optical printing method, and then the inner surface of the face plate is developed to remove the polyvinyl alcohol layer of the unexposed areas and hence leave the layer of the exposed areasThen, a light absorbing material is coated over the entire area of the inner surface of the face plate including the polyvinyl layer remaining thereon and is dried, after which the inner surface is treated with a developing solution containing hydrogen peroxide to remove the polyvinyl alcohol layers and the light absorbing material coated theron. As a result of this, thelight absorbing material remains on thoseareas where the light absorbing layer will utlimately be formed, thus providing the light absorbing layer. Thereafter, the coating, exposure and development steps are repeated for each color phosphor slurry, by which color phosphor dots are formed at desired positions surrounded by the light absorbing layer.

In the color picture tube having such a light absorbing layer, it is necessary that the ratio of the diameter 42,, of the phosphor dots and that of the apertures of light source for exposure is rotated with a predetermined radius of gyration about the apparent color centhe shadow mask satisfies the condition l-. In

prior conventional color picture tubes 1.

With prior conventional methods, in order to satisfy the condition the size of the apertures of the shadow mask serving as the exposure mask are made smaller than that in the finished tube, the phospor dots and the light absorbing layer are formed as above de scribed and then the apertures of the shadow mask are enlarged to a predetermined size as by etching. Such a method is extremely troublesome and difficult to provide for high precision in the manufacture of the color screen.

SUMMARY OF THE INVENTION This invention provides a method of making an elec-- lowing equation.

ters of the tube to provide a light pattern at the tube face on a photoresisst coating, which when developed will define phosphor dot location sites which are smaller than respective mask apertures.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are schematic diagrams, for explaining the present invention;

FIG. 3 is a graph showing the relative exposure distribution, for explaining the present invention;

FIG. 4 shows in cross section a sequence of steps employed in the manufacture of a color screen in accordance with one example of the present invention;

FIG. 5 similarly shows steps in a modified form of this invention; and

FIG. 6 is a front view showing one example of a rotary light source apparatus employed in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings the present invention will hereinafter be described. To facilitate a better understanding of this invention, a description will be given first of a light source apparatus employed in this invention in connection with FIG. 1.

In FIG. 1 reference character L indicates an ideal point light source which is turned about a point 0 with a radius r, A an aperture of a radius a formed in an optical Mask M and S a screen. The straight line joining the center of rotation of the point light source L with the center O 'of the aperture A of the optical mask M will hereinafter be referred to as the Z-axis and let it be assumed that the planes of the screen S and the mask M and the rotational plane of the point light source L lie in parallel relation to one another. The ratio of the distances between the point light source'L and the mask M and between the point light source L and the screen S is selected to be 1 2 A. The relative illumination intensity I on the area irradiated by light through the aperture A from the point light source L lying at a given rotation position (x y is expresed by the following equation.

' im- 1) +(yy1) 1 1 e A e 1, irradiated by light 0, not irradiated by light 1o. 1/) Here,

The relative exposure E (x, y) in the time T during which the point light source L is rotated with a period T and with the radius of gyration r is given by the fol- In the event that the exposure time is sufficiently long, as compared with the period T, the relative exposure is fully approximated by E in the above equation.

In the case of FIG. 1, the relative exposure E(x, y) is axissymmetrical, so that E(x, y) can be approximately obtained by the aid of FIGS. 2A to 2C geometrically.

In FIG. 2A a circle 1 indicates an area of the screen S irradiatd by light, namely an area of the screen S irradiated by light from the point light source L at the position (x y through the aperture A in FIG. 1. The center P of the circle 1 is spaced (It l)r from the Z-axis as apparent from FIG. I, and the radius of the circle 1 is ML.

The circle 1 rotates about the Z-axis and consequently a point Z with the rotation of the point light source L. Accordingly, the area of the screen S which is irradiated by light when the point light source L is rotated once is considered to lie within a circle 2 indicated by a broken line. At this time, the relative exposure in the circle 2 differs at the central area which is always irradiated by light during one rotation of the point light source L and at the peripheral area which is irradiated only while the light source L lies in a certain rotational angular range. Assume a circle 3 of a given radius R about the point Z in the circle 2. A circular arc 3A of the circle 3 inside of the circle 1 is irradiated by light but that 38 outside of the circle 1 is not irradiated. Therefore, the relative exposure E round the circumference of the circle 3 is approximately expressed in the form of the ratio of the length of the circular arc 3A and that of the entire circumference of the circle 3 as follows:

length circular arc of circle of radius contained in circle {a: ()w- 1)rl y A 11 length of circumference of circle of radius R where R V x +y Thus, the relative exposure E is distributed substantially shown in FIG. 3, the ordinate representing the relative exposure E (energy ratio of light) and the abscissa the distance R V x y) from the Z-axis on the screen S.

The curve I indicates the relative exposure when the ideal point light source L is not turned but fixed at the rotational center 0 The area irradiated by light through the aperture A is uniform in relative exposure over its entire area, so that the radius of the exposed area substantially corresponds to the diameter a of the aperture. The curve II shows the relative exposure when the point light source L is turned under the condition that the radius of gyration r is smaller than )t/lt l a, namely when the center of rotation Z of the light source L lies in the circle 1 as depicted in FIG. 2A. Further, when the radius of rotation r of the light source L increases to be equal to )t/It 1 a, namely when the circle 1 is in contact with the centerof rotation Z of the light source L as depicted in FIG. 2B, the relative exposure E becomes as indicated by the curve III. When the radius of rotation r of the light source L increases to exceed MA l a, namely when the center of rotation Z i of the light source L lies outside of the circle 1 as depicted in FIG. 2 c, the central portion of the area of the screen S corresponding to the aperture A is not irradiated by light but instead only the annular peripheral portion of the area is irradiated, with the result that the relative exposure E becomes as indicated by the curve IV.

Let it be assumed that the optimum exposure (energy ratio of light) E of a negative photoresist now usually employed is 1.0 in FIG. 3. If the radius of gyration r of the light source L is O r l a, the area of the photoresist irradiated by light through the aperture A of the mask M is a circle with a radius a, smaller than that a of the aperture A as indicated by the curve ll. Accordingly, by .suitably selecting the radius of gyration r of the light sourcev L to be in the range of 0 r }\/)t 1 a, it is possible to expose a given area which is smaller than the aperture of the exposure mask.

In the case of employing a positive type photoresist such as, for example, Az (Trademark), the radius of gyration r of the point'light source L is selected in the following manner. If r MA l a, the area of the photoresist exposed to light through the aperture A of the mask becomes annular as indicated by the curve IV, leaving unexposed the central portion which is a circle of a radius a smaller than that a of the aperture A. The unexposed central portion increases with an increase in the radius of gyration r of the light source L. Therefore, by suitable selection of the radius of gyration r of the light source L to be in the range of r )t/k I a, it is possible to irradiate an annular area leaving unexposed its central portion of a desired size smaller than the aperture of the exposure mask.

Referring now to FIGS. 4 and 5, a description will be made of the formation of the light absorbing layer and consequently the making of the color screen according to one example of this invention. FIG. 4 illustrates the case of employing a rotary light source capable of annular exposure.

The first step as shown in FIG. 4A, is to coat the entire area of the inner surface 10A of a face plate 10 of a color picture tube with a positive type photoresist 11 or a photoresist which is rendered soluble when exposed to light. Then, a shadow mask M (serving as an exposure mask) havingape'rtures A approximately 380 microns in diameter is disposed in opposing relation to the inner surface 10A of the face plate as illustrated in FIG. 4B. A light source carried in apparatus for circular movement in a plane generally at right angles to the axis of the tube which apparatus rotates a point or extended light source with a predetermined radius of gyration r, is disposed at a predetermined position opposite to the shadow mask M and then the photoresist layer 11 is irradiated by light from the light source. In this case, the radius of gyration r of the rotary light source is selected to be r )t/k I a, where l=unit distance from point source L to mask aperture unit, )t=distance from point source L to screen 10, and a=radius of aperture in shadow mask M. The radius of gyration r is of a value that when the photoresist layer 11 is exposed to light through the apertures A of mask M, the aperture being, for example, 380 microns, an unexposed central portion results which may, for example, be about 280 microns in diameter and an exposed annular portion surrounds the central portion. The center of rotation of the rotary light source is located successively at three positions, one being for exposure of a first color phosphor, for example, a green phosphor, the second for a blue phosphor and a third for a red phosphor. The three light source locations being in accordance with a usual optical printing method.

With such a rotary light source, the photoresist layer 11 is exposed to light in the form of rings or annuli 13G surrounding circular green phosphor location areas 126 about 280 microns in diameter which lie at those places where green phosphor dots will utlimately be formed as depicted in FIG. 4B.

Next, the center of rotation of the light source is shifted, for example, to the blue center of the tube and the photoresist layer 11 is similarly exposed through the apertures A at those areas 138 of annular configuration which surround circular blue phosphor location areas 128 about 280 microns in diameter lying at positions which will ultimately be occupied by blue phosphor dots as depicted in FIG. 4C. Thereafter, the center of rotation of the light source is shifted to thered center of the tube and the photoresist layer 11 is likewise exposed at those red phosphor location areas 113R of annular configuration which surround circular areas 112R about 280 microns in diameter lying at positions which will ultimately be occupied by red phosphor dots as shown in FIG. 4D.

Thereafter, the photoresist layer 111 is developed with an alkaline solution to remove all the exposed areas 13G, 13B and 13R, leaving photoresist layer 14 of the areas 12G, 12B and HR where the green, blue and red phosphor dots will be formed respectively, as illustrated in FIG. 4B.

Following the development, a graphite solution, for example, a solution of Aquadag (Trademark) is coated over the entire area of the inner surface A of the face plate including the photoresist layers 14 to form a graphite layer 15 as depicted in FIG. 4F. In the processes shown in FIGS. 48 to 4D, the photoresist layer 11 is sensitized in the form of inverted trapezoid in cross section due to a gradual increase in the absorption of light as it approaches the inner surface 10A of the face plate 10 from the surface of the photoresist layer 11, so that when developed, the photoresist layer 111 is removed in inverted trapezoidal form in cross section. At this time, edges 14a of the photoresist layers 14 are not dull but very sharp because the layers 14 are in the inverted trapezoidal form in cross section. The sharpness of the edges Ma affects the accuracy of the phosphor dots which will be subsequently formed, so that in the illustrated example the phosphors can be formed with high accuracy.

Then, the outer surface of the face plate 10 is irradiated by light as indicated by the arrows 16 in FIG. 4F to sensitize the photoresist layers 14, after which the inner surface of the face plate 10 is developed with an alkaline solution to remove the photoresist layers 14 and the graphite layer 15A coated theron, providing a light absorbing layer 17 on the inner surface 10A of the face plate 10 at those areas where the phosphor dots will not ultimateley be formed, as illustrated in FIG. 40.

Subsequent to the formation of the light absorbing layer 17, a usual, for example, green phosphor slurry 18G is coated over the entire area of the inner surface 10A of the face plate 10 including the light absorbing layer 17 and is exposed to light through the aforementioned masked M by a usual light source fixed at the socalled green center of the tube as shown in FIG. 4H. In this case, those areas of the green phosphor slurry layer 18G which are irradiated by light through the apertures A of the mask M are greater than the areas to be subsequently occupied by green phosphor dots and partly cover the light absorbing layer adjacent thereto as clearly shown in the figure. The inner surface 10A of the face plate 10 is then developed to provide green phosphor dots 19G smaller than the apertures A at predetermined areas surrounded by the light absorbing layer 17 as illustrated in FIG. 4L

In a similar manner, a blue phosphor slurry is coated on the inner surface of the face plate, exposed to light through the mask by the light source shifted to the aforementioned so-called blue center of the tube and developed, thereby to provide blue phosphor dots 198 at predetermined areas surrounded by the light absorb.- ing layer. Further, a red phosphor slurry is likewise coated on the inner surface of the face plate, exposed to light through the mask by the light source positioned at the so-called red center of the tube and developed to provide red phosphor dots 19R at predeterminend areas surrounded by the light absorbing layer. Thus, a color screen 20 having the light absorbing layer 17 is provided. A thin aluminum coating 22 is formed on the color screen 20 through an intermediate film 21 of acrylate resin as shown in FIG. 4]. The intermediate film 211 is removed by baking and hence does not exist in the finished tube.

With the method of the present invention described above, the use of the rotary light source enables the formation of the light absorbing layer 17 having void areas smaller in diameter than the apertures of the shadow mask, in which the color phosphor dots are formed. Therefore, the present invention can dispsense with the conventional process for enlarging the apertures of the shadow mask after the formation of the light absorbing layer and the color phosphor dots and provides for enhanced precision in the making of the light absorbing layer and the color screen. Further, the rotation of the light source provides a concentric ideal distribution of light on the color screen, and hence allow ease in the making of a correcting filter.

In addition, the rotation of the light source permits the use of either a point or extended light source and does not necessitate the provision of a point light source by the use of focusing lens, so that the light source can be used directly, thereby to increase the rate of utilization of light necessary for printing.

Where the radius of gyration r of the light source is selected such that r )t/A 1 a, use is made of the positive type photoresist which when exposed to light is rendered soluble, so that control of the exposure need not be so accurate, allowing ease in exposure. Further, since the positive type photoresist is removed in inverted trapezoidal form in cross section in the fonnation of the light absorbing layer as previously described, the edges of the photoresist layer are so sharp that the light absorbing layer and the color phosphor dots are formed with accuracy.

Further in accordance with this invention, where it is desired to form, for example, the green phosphor dots larger than the other color phosphor dots because of the darkness of the former, it is sufficient only that in the exposure for the green color during the formation of the light absorbing layer, the radius of gyration of the light source is selected to be greater than those for the other colors (in the case of r MA l a). Also in this case, the formation of the green phosphor dots is simple and accurate.

FIG. 5 illustrates a modified form of this invention, which employs a rotary light source of a radius of gyration such that r )t/k 1a. The first step is to coat the inner surface 30A of a face plate 30 over its entire area with a negative type photoresist or a photoresist 31 which when exposed to light is rendered insoluble, as depicted in FIG. 5A.

Then, a shadow mask M having apertures A approximately 380 microns in diameter is mounted on the inner surface A of the face plate 30 and a rotary light source apparatus provided with a point or extended light source rotating with a predetermiend radius of gyration r is disposed at a predetermined position in opposing relation to the shadow mask M. The photoresist layer 31 is exposed to light from the rotary light source. In this case, the radius of gyration r of the rotary light source is selected to be smaller than k/k l a as previously described so that the area exposed through the aperture A, for example, about 380 microns in diameter may be approximately 280 microns in diameter. The center of rotation of the light source corresponds to the position of the point light source for exposing a first color phosphor, for example, the green phosphor in the usual optical printing method, namely to the socalled green center of the tube.

With such a rotary light source, the photoresist layer 31 is exposed to light at those areas 32G having a diameter of 280 microns which will eventually be occupied by green phosphor dots. Then, the center of rotation of the light source is shifted to, for example, the so-called blue center of the tube, namely, the position for exposing the bluephosphor in the conventional optical printing method and the photoresist layer 31 is exposed to light to be sensitized at those areas 328 having a diameter of 280 microns which will subsequently be occupied by blue phosphor dots. Next, thecenter of rotation of the light source is shifted to the so-called red center of the tube to sensitize those areas 32R having a diameter of 280 microns which will ultimately be occupied by red phosphor dots, as shown in FIG. 5B.

Thereafter, the photoresist layer 31 is developed with water to remove that area which has not been exposed, thereby to provide on the inner surface of the face plate photoresist layers 33 at those areas which have been exposed and will utlimately occupied by the green, blue and red phosphor dots. Next, graphite 34 is coated over the entire area of the inner surface 30A of the face plate 30 including the photoresist layers 33 as depicted in FIG. 5C and is then developed again with a hydrogen peroxide solution to remove the photoresist layers 33 and the graphite layer 340 coated thereon, thus forming a light absorbing layer 35 on the inner surface 30A of the face plate 30 at those areas where the color phospor dots will not be formed, as illustrated in FIG. 5D.

Following this, for example, a usual green phosphor slurry 36G is laid down over the entire area of the inner surface 30A of the face plate 30 with the light absorbing layer 35 formed thereon and is exposed to light through the aforementioned shadow mask M by a light source fixed at the so-called green center of the tube, as shown in FIG. 5E. In this case, light from the light source irradiates through the apertures A of the mask M those areas to be ultimately occupied by the green phosphor dots and partly the light absorbing layer surrounding them. After exposed, the green phosphor slurry 36G is developed to provide green phosphor dots 37G only at desired positions as shown in FIG. 5F.

Similarly, a blue phosphor slurry 36B is coated on the inner surface 30A of the face plate 30 and is exposed to light by the light source located at the so-called blue center of the tube, thereafter being developed to form blue phosphor dots 373 at desired positions surrounded by the light absorbing layer 35 as depicted in FIGS. 5G and 5H. Then, a red phosphor slurry 36R is likewise coated on the inner surface 30A of the face plate 30 and is then exposed to light by the light source disposed at the so-called red center of the tube as shown in FIG. 51, thereafter being developed to form red phosphor dots 37R at desired positions. Thus, a color screen 38 having the desired light absorbing layer 35 is produced.

A thin aluminum coating 40 is formed on the color screen 38 through an intermediate film 39.

Also in this example, the phosphor dots of one of the colors can be formed to be of a desired diameter greater than those of the other color phosphor dots by selecting the radius of gyration of the light source for the exposure of said one color phosphor to be smaller than that for the exposure of the other color phosphors.

FIG. 6 illustrates one example of the rotary light source apparatus for use in this invention which is adapted to rotate the light source with a desired radius of gyration.

Reference numeral 140 indicates a lamp house enclosing a point or extended light source 41 made up of, for example, a superhigh-pressure mercury-arc lamp. The lamp house 140 is mounted on a support 42 and effectively serves as a point light source. Under the support 42 there is disposed a first shift means 43 which rotates with the support 42 but slides the support 42 and consequently the lamp house 140 in the x-direction (to right and left in the figure) and the y-direction (a direction perpendicular to the plane of the sheet of the drawing), the first shift means 43 being mounted on a rotary unit 45 as a unitary structure therewith which is rotatable about a fixed shaft 44. The rotary unit 45 has mounted thereon a pulley 47', which is driven by a synchronous motor 46 through a belt 47. The first shift means 43 consists of a first-support base plate 48 supporting the lamp house support 42 slidably in the y and a second support base plate 49 which is formed as a unitary structure with the rotary unit 45 supporting the first support base plate 48 slidably in the x-direction. By adjusting a first micrometer 50, the lamp house support 42 is moved in the y-direction and consequently the light source 41 is moved in the y-direction. Further, by adjusting a second micrometer 51, the first support base plate 48 is moved in the x-direction to carry the light source 41 in that direction. That is, the radius of gyrotation r of the light source 41 is determined by the micrometers 50 and While the fixed shaft 44 is secured to a support 52, which is, in turn, attached to a base 54 through a second shift means 53 capable of freely moving the fixed shaft 44 in the xand y-directions. The second shift means 53 is identical in construction with the aforementioned first shift means 43. Reference numerals 55 and 56 designate micrometers for moving the fixed shaft 44 in the yand x-direction. Namely, the second shift means 53 is to determine the center of rotation of the light source 41.

Further, the lamp house is provided with a cooling device for cooling the light source 41. That is, an

inlet pipe 57 for introducing a cooling water into the lamp house 140 and an outlet pipe 58 for discharging the cooling water therefrom are coupled to the lamp house 140 as shown in the figure. The lamp house 140 is adapted to be controlled by the presence of the inlet and outlet pipes 57 and 58 in such a manner that it is not rotated continuously in the same direction but is reversed after one rotation to effect sufficient exposure with one reciprocation of rotation of the light source 41. Reference numeral 59 indicates a micro-switch for controlling the reversal of the motor which is disposed between the rotary unit 45 and the fixed support 52.

Further, the base 54 has attached thereto a third shift means 60 for shifting the light source to particular positions for the exposure of the respective three color phosphors. The third shift means 60 is designed to slide in the xand y-directions as is the case with the first and second shift means 43 and 53. Reference numeral 61 identifies a correcting lens and 62 a face plate.

' With such a light source apparatus, a desired rotarylight source rotating with a desired radius of gyration r can be obtained by determining the center of rotation of the light source 41 with the second shift means 53 and locating the light source 411 at a position spaced a desired distance Y from its center of rotation. After exposure of a first color phosphor, the third shift means 60 is adjusted to shift the light source 41 to the particular positions for exposing the other second and third color phosphors respectively.

It will be apparent that many modifications and varia- DEFINITIONS A screen shall be deemed to mean a mosaic of phospor dots formed on the face of a color television tube or the like in a mosaic pattern in multi-color groupings, such as red, green and blue.

A shallow mask shall be deemed. to be a sheet member, having a very large number of apertures therein, which is mounted in front of a screen.

The color centers of a tube shall be deemed to mean the apparent source of origin of an electron beam passing through a particular aperture of the mask. This apparent source of origin will differ slightly for different colors due to the different positions of the color guns in the color television tube.

A photoresist material is one which when portions thereof are exposed to light, such portions are rendered soluble or insoluble in a preselected solution depending on whether the photoresist material is a positive or negative type. Such photoresists are well known in the art.

A light absorbing material shall be deemed to mean a relatively dark surface material such as graphite, such for example as one formed by a solution of Aquadag (Trademark).

Where holes are said to be formed in a light absorbing material layer, it refers to areas where no portion of the light absorbing material layer covers the face of the tube.

In mathematical expressions, the distance from the light source to an aperture in the shadow mask is expressed as a unit distance and the distance from the light source to the screen is expressed in such units.

Gyration of the light source about a color center shall be deemed to mean movement of the light source about the apparent path of the electron beam which will subsequently emanate from that particular color gun.

We claim as our Invention:

1. In the manufacture of a color screen for a color picture tube having a shadow mask with apertures therein, the method which includes:

depositing a layer of photoresist material of the positive type over the face of the tube;

mounting a shadow mask having apertures of the same diameter as the shadow mask of the finished tube in spaced relation in front of said face of said tube;

irradiating light on said layer through said apertures of said mask, successively rotating the source of said light about the different apparent color centers of the tube, the radius of gyration being such as to form an annulus of light, and

wherein the radius r of gyration is selected as r )t/lI 1 a; wherein A is the ratio of the light source-toface plate spacing to the light source-to-mask spacing and a is the radius of said apertures,

thereafter developing the photoresist layer to remove the portions thereof where'the annulus of light fell;

coating a graphite solution over the entire area of the face of said tube including the remaining portions of the photoresist layer; I irradiating the opposite face of the face plate of said tube by light to sensitize the said remaining portions of said photoresist layer and the portions of the graphite layer overlying the said remaining portions of the photoresist layer, thereafter developing said remaining portions of said photorersist to remove it with the graphite layer overlying thereof; and I coating the regions of the face plate not now cov ered by the graphite layer with phosphor slurry of desired colors to form a mosaic of multi-colored groupings on the face of said tube.

2. In the method of claim l,wherein said apertures are larger in diameter than the portions remaining where said annulus of light did not fall.

3. In the manufacture of a color screen for a color picture tube having a shadow mask having apertures therein, the method which includes:

depositing a layer of photoresist material of a negative type over the face of a tube;

mounting a shadow mask with apertures of the same diameter as the shadow mask of the finished tube in spaced relation in front of said face of said tube;

irradiating light on said layer through said apertures of said mask, successively rotating the source of said light about the different apparent color centers of the tube, the radius of gyration being such as to form a spot of light on said tube face which is smaller than the apertures of said mask through which the light passes, and

wherein the radius r of gyration is selected as 0 R )t/)t l a, where )t is the ratio of the light source-to-face plate spacing to the light source-tomask spacing and a is the radius of said apertures,

thereafter developing the photoresist layer to remove the portions thereof where the spot of light did not fall;

sired colors to form a mosaic of multi-colored grouping on the face of said tube. 4. In the method of claim 3, wherein said apertures are larger in diameter than the portions of light where said annulus of light did not fall. 

1. IN THE MANUFACTURE OF A COLOR SCREEN FOR A COLOR PICTURE TUBE HAVING A SHADOW MASK WITH APERTURES THEREIN, THE METHOD WHICH INCLUDES: DEPOSITING A LAYER OF PHOTORESIST MATERIAL OF THE POSITIVE TYPE OVER THE FACE OF THE TUBE; MOUNTING A SHADOW MASK HAVING APERTURES OF THE SAME DIAMETER AS THE SHADOW MASK OF THE FINISHED TUBE IN SPACED RELATION IN FRONT OF SAID FACE OF SAID TUBE; IRRADIATING LIGHT ON SAID LAYER THROUGH SAID APERTURES OF SAID MASK, SUCCESSIVELY ROTATING THE SOURCE OF SAID LIGHT ABOUT THE DIFFERENT APPARENT COLOR CENTERS OF THE TUBE, THE RADIUS OF GYRATION BEING SUCH AS TO FORM AN ANNULUS OF LIGHT, AND WHEREIN THE RADIUS R OR GYRATION IS SELECTED AS R>N/N - 1 A; WHEREIN N IS THE RATIO OF THE LIGHT SOURCE-TO-FACE PLATE SPACING TO THE LIGHT SOURCE-TO-MASK SPACING AND A IS THE RADIUS OF SAID APERTURES, THEREAFTER DEVELOPING THE PHOTOREIST LAYER TO REMOVE THE PORTIONS THEREOF WHERE THE ANNULUS OF LIGHT FELL; COATING A GRAPHITE SOLUTION OVER THE ENTIRE AREA OF THE FACE OF SAID TUBE INCLUDING THE REMAINING PORTIONS OF THE PHOTORESIST LAYER; IRRADIATING THE OPPOSITE FACE OF THE FACE PLATE OF SAID TUBE BY LIGHT TO SENSITIVE THE SAID REMAINING PORTIONS OF SAID PHOTORESIST LAYER AND THE PORTIONS OF THE GRAPHITE LAYER OVER-
 2. In the method of claim 1, wherein said apertures are larger in diameter than the portions remaining where said annulus of light did not fall.
 3. In the manufacture of a color screen for a color picture tube having a shadow mask having apertures therein, the method which includes: depositing a layer of photoresist material of a negative type over the face of a tube; mounting a shadow mask with apertures of the same diameter as the shadow mask of the finished tube in spaced relation in front of said face of said tube; irradiating light on said layer through said apertures of said mask, successively rotating the source of said light about the different apparent color centers of the tube, the radius of gyration being such as to form a spot of light on said tube face which is smaller than the apertures of said mask through which the light passes, and wherein the radius r of gyration is selected as 0<R< lambda / lambda - 1 a, where lambda is the ratio of the light source-to-face plate spacing to the light source-to-mask spacing and a is the radius of said apertures, thereafter developing the photoresist layer to remove the portions thereof where the spot of light did not fall; coating a graphite solution over the entire area of the face of the tube; removing the remaining portion of the photoresist layer; and coating the regions of the face plate not now covered by the graphite layer with phosphor slurry of desired colors to form a mosaic of multi-colored grouping on the face of said tube.
 4. In the method of claim 3, wherein said apertures are larger in diameter than the portions of light where said annulus oF light did not fall. 